for the manual.
Adventure is a 1979 maze video game for the Atari 2600 video game console and is considered the first action-adventure game. Its creator, Warren Robinett, introduced the first widely known Easter egg to the gaming world.
Adventure was published by the console's developer, Atari, Inc. It was inspired by a computer text game, Colossal Cave Adventure, created by Will Crowther and later modified by Don Woods. Despite discouragement from his boss at Atari who said it could not be done, game designer Warren Robinett created a graphic game loosely based on the text game. Atari's Adventure went on to sell a million copies, making it the seventh best selling Atari 2600 game. At the time of the game's creation Atari did not credit any of its authors for their work. Robinett included a hidden message in the game identifying himself as the creator, thus creating one of the earliest known Easter eggs in a video game. It took up 5% of the storage space on the cartridge. Atari found out about the Easter egg when it received a letter from a fifteen-year-old player, but left it in the game, partially due to the expense of creating a new read-only memory (ROM) mask, or memory chip, which was $10,000 US in the early years after the game's release.
The total memory used by the game program was 4096 bytes (4 KB) for the game code (in ROM) and 128 bytes for program variables (in RAM). The Atari 2600's CPU was a 1.19 megahertz 8-bit MOS Technology 6507, which was a cheaper version of the 6502. Because of a limitation in the Atari 2600's hardware, the left and right sides of nearly every screen are mirror images of each other, which fostered the creation of the game's confusing mazes. The notable exceptions are two screens in the black castle catacombs and two in the main hallway beneath the Gold Castle. These two hallway screens are mirrored, but contain a vertical "wall" object in the room in order to achieve a non-symmetrical shape, as well as act as a secret door for an Easter egg.
Adventure was the first action-adventure game on a video console, the first to contain a widely known Easter egg, and the first to allow a player to have a stash of items, which required the player to select which one to use at any given moment, usually through keyboard or joystick input. Adventure allowed the player to drop one item and pick up another without having to type in any commands. The game was also the first to use a fog of war effect in its catacombs, which obscured most of the playing area except for the player's immediate surroundings.